This project seeks to determine the role of plasma membrane lipids in the regulation of lens epithelial cell division and differentiation. Turnover of phosphatidylinositol and polyphosphoinositides has been shown to increase markedly within seconds after the addition of growth factors to quiescent lens epithelial cells. Thereafter, the rate of cell division is proportional to the rate of phosphoinositide degradation. A similar correlation between phosphatidylinositol degradation and cell division has been observed in embryonic chicken lens epithelia during development. Since phosphatidylinositol is rich in arachidonic acid, the arachidonic acid metabolites synthesized by cultured lens epithelial cells have been characterized in an effort to understand the physiological role of phosphatidylinositol degradation. A unusual metabolite of arachidonic acid has been isolated which is mitogenic for cultured lens cells. Specific alterations in phosphatidylinositol metabolism are being correlated with the levels of insulin receptors and IGF receptors present in embryonic chicken lens epithelia at different developmental stages.